Method for communicating and radio station therefor

ABSTRACT

The present invention relates to method for communicating between a primary station and a secondary station comprising
         (a) at the secondary station, upon arrival of a data packet to be transmitted to the primary station, buffering said data packet in a buffer, and transmitting to the primary station a request for an uplink transmission resource if a request condition is satisfied, said request condition being based on at least one previous grant of uplink transmission resource,   (b) at the primary station, granting to the secondary station an uplink transmission resource to be used.

CLAIM OF PRIORITY

This Application is a Continuation of application Ser. No. 12/933,688, filed Sep. 21, 2010, which is a National Stage of International Application PCT/IB2009/051066, filed Mar. 16, 2009, which claimed foreign priority of EPO 08305065.8 filed Mar. 21, 2008, all of which are incorporated herein in whole by reference.

FIELD OF THE INVENTION

The present invention relates to a method for communicating in a network. More specifically, the present invention relates to communication between a primary station and a secondary station, in a telecommunication network, like a cellular telecommunication network (e.g. UMTS, GSM).

BACKGROUND OF THE INVENTION

In a cellular network, each cell comprises a primary station, like a base station, or a Node B, or an eNB communicating with a plurality of secondary stations, like mobile stations, or User Equipments. To be able to send data to the primary station on some uplink channels, a secondary station must have an allocated resource (time slot, frequency subcarrier, and/or code or likewise).

Many communication systems operate using a centralised scheduler which is responsible for allocating transmission resources to different nodes. A typical example is the uplink of the UMTS LTE (Long Term Evolution), where the uplink transmissions from different secondary stations are scheduled in time and frequency by the primary station. The primary station transmits a “scheduling grant” message to a secondary station, indicating a particular time-frequency resource for the secondary station's transmission, typically around 3 ms after the transmission of the grant message. The grant message also typically specifies transmission parameters as the data rate and/or power to be used for the secondary station transmission.

In order for the primary station to issue appropriate grants, it needs to have sufficient information about the amount and type of data awaiting transmission in the buffer of each secondary station.

In LTE, several types of buffer status report (BSR) messages are therefore defined, which may be transmitted from a secondary station to the primary station when certain triggers occur. The current version of 3GPP TS36.321 is incorporated by reference.

The Buffer Status reporting procedure is used to provide the serving primary station with information about the amount of data in the uplink buffers of the secondary station. Two kinds of Buffer Status Reports are used depending on the events. A short Buffer Status Report (BSR) comprises the identity of a single group of logical channels, together with a 6-bit indicator of the amount of data corresponding to that group of logical channels currently residing in the secondary station buffer awaiting transmission. A long BSR comprises 4 concatenated short BSRs, each corresponding to a different group of logical channels.

A problem with the BSR procedure defined above is that a secondary station is only permitted to transmit a BSR if it has a granted resource in which to transmit. If new data arrives in a secondary station's buffer and the secondary station has no granted resource in which to transmit the data or to send a BSR to indicate that it has data awaiting transmission, the secondary station must either wait until a grant is received, or transmit a simpler version of the BSR which can be transmitted using some specially-designated resources which can be used without a specific granted resource. This simpler version of the BSR is known as a “scheduling request” (SR), and typically comprises only a single bit to indicate that data is in the buffer. It is also known for an SR to comprise a small plurality of bits, which gives greater functionality. In response to receiving an SR, a primary station may either transmit a grant allocating a suitable amount of transmission resource for the secondary station then to send a BSR, or transmit a grant allocating a larger amount of transmission resource which would enable the secondary station to transmit some data in addition to the BSR; however, in the latter case there is typically no means for the primary station to determine a suitable size of allocation to make, unless the SR comprises more than a single bit.

In a known implementation, a secondary station without an uplink transmission grant sends an SR as soon as data arrives in its buffer. However, this is inefficient and wasteful of resources if the primary station would in any case provide a grant within an acceptable delay.

However, if the secondary station were always to refrain from transmitting an SR and to wait for a grant to be received, Quality of Service (QoS) criteria could be breached if the primary station did not provide a grant within an acceptable delay.

SUMMARY OF THE INVENTION

It is an object of the invention to propose a method for communicating in network which alleviates the above mentioned problem.

Another object of the invention is to propose a method which permits to indicate to the primary station to be aware of the state of the buffer of the secondary stations without creating too much overhead.

Still another object of the invention is to propose a method reducing the unnecessary transmission of scheduling requests, while allowing QoS requirements to be satisfied. It is required that uplink data transmission occurring within specified latency contraints.

To this end, it is proposed a method for communicating between a primary station and a secondary station comprising

-   -   (a) at the secondary station, upon arrival of a data packet to         be transmitted to the primary station, buffering said data         packet in a buffer, and transmitting to the primary station a         request for an uplink transmission resource if a request         condition is satisfied, said request condition being based on at         least one previous grant of uplink transmission resource,     -   (b) at the primary station, granting to the secondary station an         uplink transmission resource to be used.

As a consequence, this prevents the secondary station from transmitting unnecessary scheduling requests. Indeed, only if an uplink transmission resource is not received during said time period, the secondary station sends a scheduling report. Moreover, the time period may be adjusted in accordance to events or conditions of transmission.

The present invention also relates to a secondary station comprising

-   means for transmitting data to a primary station on an uplink     channel, -   buffering means for buffering data packets to be transmitted to the     primary station upon arrival of said data packets,     -   means for requesting, if a request condition is satisfied, the         primary station to grant an uplink transmission resource, said         request condition being based on at least one previous grant of         uplink transmission resource.

According to another aspect of the invention, a system comprising at least one secondary station in accordance with the first aspect of the invention and a primary station, said primary station comprising means for granting to the secondary station an uplink transmission resource.

These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawing, wherein:

FIG. 1 is a block diagram of a system in accordance with the invention comprising a primary station and at least a secondary station.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for communicating in a network, like a cellular network. For instance, the network may be a UMTS network as depicted on FIG. 1.

Referring to FIG. 1, a radio communication system in accordance with the invention comprises a primary station (BS) 100 and a plurality of secondary stations (MS) 110. The primary station 100 comprises a microcontroller (μC) 102, transceiver means (Tx/Rx) 104 connected to antenna means 106, power control means (PC) 107 for altering the transmitted power level, and connection means 108 for connection to the PSTN or other suitable network. Each MS 110 comprises a microcontroller (μC) 112, transceiver means (Tx/Rx) 114 connected to antenna means 116, and power control means (PC) 118 for altering the transmitted power level. Communication from primary station 100 to mobile station 110 takes place on a downlink channel, while communication from secondary station 110 to primary station 100 takes place on an uplink channel.

According to a first embodiment of this invention, it is provided a means to control the circumstances in which a secondary station sends a Scheduling Request (SR) or a request of resource, in order to avoid unnecessary transmission of SRs, while also allowing QoS requirements to be satisfied (i.e. uplink data transmission occurring within specified latency constraints).

In accordance with this first embodiment of the invention, a secondary station which does not have an uplink grant may also transmit an SR in response to data arriving in its buffer, if the secondary station can determine that the primary station is not likely to provide a grant within an acceptable time delay (and otherwise the secondary station refrains from sending an SR or waits for some time duration to elapse before sending an SR).

The secondary station sends an SR at the earliest opportunity if the time since the last grant is greater than a threshold in a first example of this embodiment.

In another example of this embodiment, the condition which must be satisfied is that average time between previous grants in a given time window is greater than a threshold. This permits to have more equity between all the secondary stations.

In another example, the size of resource (measured in e.g. bits) allocated in the previous grant is less than a threshold, or the average size of resource allocated in a predetermined number of previous grants or in all the previous grants received in a given time window is less than a threshold. Similarly, the total amount of resource allocated in a predetermined number of previous grants or in all the previous grants received in a given time window is less than a threshold.

In the above examples, the thresholds may be predetermined This threshold may be for example transmitted to the secondary station by means of a signaling channel. For instance, the primary station sends on a control channel the time duration of the threshold.

But to obtain a system which is more appropriate to each situation, the threshold may be dependent on characteristics. In an example of this embodiment, the threshold depends on one or more data characteristic of the data which had arrived in the buffer. Some examples of suitable data characteristics include:

-   -   an indication of the priority of the data;     -   QoS parameters of the data (e.g. latency requirements, or a         function thereof)     -   an identity of a logical channel or group of logical channels to         which the data is assigned;     -   the amount of data which had arrived in the buffer;     -   the amount of data in the buffer;     -   the rate of arrival of data in the buffer;     -   the time since the previous arrival of data in the buffer.

Thus, if the data is of high priority, or if the amount of data in the buffer or the amount of data which had arrived is great, then the threshold is lower.

In another example, the threshold depends on whether or not a cell change has occurred within a preceding time period. If a cell change has occurred within a preceding time period, the threshold may be lowered.

In still another example, the threshold is based on the time elapsed since the secondary station last requested a resource by sending an SR or sending a BSR without receiving a corresponding grant. If no resource has been allocated to the secondary station for a long time, it may be urgent to provide resource to this secondary station, so the threshold is lowered to enable the secondary station to request such resource.

In another example of this embodiment, the threshold determination method takes into account one or more characteristics of the radio channel. Indeed, if the radio channel conditions are not good, it may be interesting for the secondary station to wait before asking for resource. Examples of radio channel characteristics that can be used to simply estimate the conditions of the radio channel are given below:

-   -   the rate at which the secondary station could transmit data         under the current channel conditions,     -   the current uplink transmission power requested by the primary         station—e.g. a high power could be an indicator of poor channel         quality;     -   An estimate of the downlink channel channel quality as an         indicator of uplink channel quality (especially in a TDD         system).

A combination of any of the above—e.g. a threshold set on the basis of priority of data, but modified according to uplink channel quality—for example, if the channel quality is good but the UE has not received a grant for a long period, it could be inferred that the absence of a grant is not due to poor channel quality and therefore the threshold for sending an SR could be set lower.

Note that in some embodiments the criteria used to determine whether an SR is transmitted may depend on at least one characteristic of the data, examples of which are:

-   -   an indication of the priority of the data;     -   QoS parameters of the data (e.g. latency requirements, or a         function thereof)     -   an identity of a logical channel or group of logical channels to         which the data is assigned;     -   the amount of data which had arrived in the buffer;     -   the amount of data in the buffer;     -   the rate of arrival of data in the buffer;     -   the time since the previous arrival of data in the buffer.

Note also that an embodiment in which the secondary station sends an SR if the total amount of resource allocated in all the previous grants received in a given time window is less than a threshold, where the threshold is derived from the amount of data which had arrived in the buffer, amounts to a situation where the secondary station determines that the data which has arrived in the buffer exceeds that which the primary station has historically expected—in other words, the data which has arrived in the buffer is probably outside the knowledge of the primary station.

A particular example of this embodiment could comprise a configuration in which the primary station configured persistently-scheduled uplink transmission resources corresponding to a regular arrival rate of packets in the secondary station's buffer—for example for a VoIP application. If a packet arrived in the secondary station's buffer at a different time from one of the usual VoIP time instants corresponding to the persistent schedule, the secondary station would send an SR, whereas a packet arriving in accordance with the persistent schedule of granted resources would not trigger an SR.

In another similar embodiment, if a packet arrived in the secondary station's buffer with a larger size than usual the secondary station would send an SR to request additional resources. Whereas a packet arriving with a size in accordance with the persistent schedule of granted resources would not trigger an SR.

In one embodiment of this invention, a primary station receives grants to transmit data from time to time. When a new data packet arrives in the secondary station's buffer, the secondary station checks the priority of the data packet, and if the priority is higher than a first threshold and the elapsed time since the last received grant is longer than a second threshold, the secondary station sends an SR; otherwise the secondary station refrains from sending an SR. The second threshold may be a function of the priority—for example, the allowed time delay could be longer for low-priority data.

In another embodiment of this invention, a secondary station receives grants to transmit data from time to time. When a new data packet arrives in the secondary station's buffer, the secondary station checks the amount of data in the data packet, and if the amount of data is higher than a first threshold and the elapsed time since the last received grant is longer than a second threshold, the secondary station sends an SR; otherwise the secondary station refrains from sending an SR. The second threshold may be a function of the amount of data—for example, the allowed time delay could be longer for small amounts of data.

According to another embodiment of the invention, a secondary station which does not have an uplink grant when data arrives in its buffer waits for a given delay period before it transmits an SR, after a first SR if any transmitted in accordance with the first embodiment of the invention . If a grant is received during this period, the secondary station refrains from transmitting an SR, and uses the transmission resources provided by the received grant.

In examples of this embodiment, the delay or time period before transmitting an SR may be determined according different methods. In a first variant, this delay is of a predetermined duration. This duration may be transmitted to the secondary station by means of a signaling channel. For instance, the primary station sends on a control channel the time duration.

In another variant, this duration may correspond to one or more data characteristic, i.e characteristics of data which had arrived in the buffer. This permits to have an appropriate time delay to each situation. These data characteristics may be for instance:

-   -   an indication of the priority of the data;     -   QoS parameters of the data (e.g. latency requirements, or a         function thereof)     -   an identity of a logical channel or group of logical channels to         which the data is assigned, an identity of a kind of data;     -   the amount of data which had arrived in the buffer;     -   the total amount of data in the buffer;     -   the rate of arrival of data in the buffer;     -   the time since the previous arrival of data in the buffer.

Thus, if the data is of high priority, or if the amount of data in the buffer or the amount of data which had arrived is great, then the time duration is shorter.

In another example, the time delay is based on any change of cell. If a cell change has occurred within a preceding time period, the time period duration may be shortened.

In still another example, the time period duration is based on the time elapsed since the secondary station last requested a resource by sending an SR or sending a BSR without receiving a corresponding grant. If no resource has been allocated to the secondary station for a long time, it may be urgent to provide resource to this secondary station, so the time period is shortened.

In another example of this embodiment, the time period duration takes into account one or more characteristics of the radio channel. Indeed, if the radio channel conditions are not good, it may be interesting for the secondary station to wait before asking for resource. Examples of radio channel characteristics that can be used to simply estimate the conditions of the radio channel are given below:

-   -   the rate at which the secondary station could transmit data         under the current channel conditions;     -   the current uplink transmission power requested by the primary         station—e.g. a high power could be an indicator of poor channel         quality;     -   an estimate of the downlink channel quality as an indicator of         uplink channel quality (especially in a TDD system).

In one embodiment of this invention, a secondary station receives grants to transmit data from time to time. When a new data packet arrives in the secondary station's buffer, the secondary station checks the priority of the data packet, and waits for a time period corresponding to the priority of the data packet before sending an SR. For example, if the priority of the data is high, the secondary station would wait for a shorter time period than if the priority of the data is low. In any case, if a grant is received during the time period, the secondary station refrains from sending an SR.

In another embodiment of this invention, a secondary station receives grants to transmit data from time to time. When a new data packet arrives in the secondary station's buffer, the secondary station checks the amount of data in the data packet, and waits for a time period corresponding to the amount of data before sending an SR. For example, if the amount of data is high, the secondary station would wait for a shorter time period than if the amount of data is low. In any case, if a grant is received during the time period, the secondary station refrains from sending an SR.

This invention may be used in communication systems utilizing centralized scheduling, such as UMTS and LTE, Mobile terminals for use in such systems or Hubs which route calls from multiple terminals to base stations. Such devices would appear like a UE from the point of view of the network.

It is to be noted that the present invention is not limited to the examples described above and can be adapted. For instance, it is to be understood that in some adaptations, the role of the primary station may be a mobile station and the secondary station may be a base station. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. 

The invention claimed is:
 1. A method, executable by a processor within a secondary station for the communication of data and control information with a primary station, said method comprising: receiving control information from the primary station; and when, at a current time, data is available in a buffer for uplink transmission and a grant of uplink resource for transmission of data is not available to transmit said available data, determining a time of a most recent, with respect to said current time, previous buffer status report that was made using resources granted by a previous grant of uplink resources, determining a difference between said current time and said time of said most recent previous buffer status report; and transmitting a request for uplink resources when said difference exceeds a threshold.
 2. The method claim 1, wherein said request for uplink resources is a scheduling request (SR).
 3. The method of claim 1, wherein said threshold is predetermined.
 4. The method of claim 1, further comprising: receiving information indicative of said threshold from said primary station.
 5. The method of claim 1, wherein said threshold is determined based on at least one characteristic of said available data.
 6. The method of claim 1, wherein said threshold is determined based on at least one characteristic of a communication channel between the primary station and the secondary station.
 7. The method of claim 6, wherein said channel is one of: an uplink channel and a downlink channel.
 8. A secondary station configured to communicate with a primary station, the secondary station comprising: a transceiver configured to receive control information from the primary station; and a processing circuit, coupled to said transceiver, configured to: when, at a current time, data is available for uplink transmission and a grant of uplink resource for transmission is not available to transmit said available data, determine a time of a most recent, with respect to said current time, previous buffer status report that was made using resources granted by a previous grant of uplink resources, determine a difference between said current time and said time of said most recent previous buffer status report; and transmit, through said transceiver, a request for uplink resources when said difference exceeds a threshold.
 9. A secondary station comprising: a buffer; a timer; and a transceiver being configured to receive control information from a primary station and being further configured to transmit a scheduling request when: the timer indicates that a time since the transmission of the latest status report for the buffer, which was transmitted using uplink resources of a previously received uplink transmission resource grant, exceeds a prescribed time, and the buffer contains data for transmission, and no uplink transmission resource grant has been received since transmission of the buffer status report.
 10. The secondary station of claim 9, wherein said scheduling request (SR) is a request for uplink resources.
 11. The secondary station of claim 9, wherein said prescribed time is predetermined.
 12. The secondary station of claim 9, wherein the transceiver receives information indicative of said prescribed time from a primary station.
 13. The secondary station of claim 9, wherein said prescribed time is determined based on at least one characteristic of said data for transmission.
 14. The secondary station of claim 9, wherein said prescribed time is determined based on at least one characteristic of a communication channel between said secondary station and said primary station.
 15. The secondary station of claim 14, wherein said communication channel is one of: an uplink channel and a downlink channel.
 16. The secondary station of claim 9, wherein the scheduling request is sent at the earliest opportunity after the time since the transmission of the most recent buffer status report which was transmitted using uplink transmission resources of a previously received uplink transmission resource grant, exceeds a prescribed time.
 17. The secondary station of claim 9, wherein the prescribed time is changed when the secondary station changes cell connection.
 18. A method for requesting uplink transmission resources from a primary station by a secondary station, comprising: receiving control information from the primary station; transmitting a request for uplink transmission resources after transmission of a most recent, with respect to a current time, buffer status report when: a time since the transmission of the most recent buffer status report which was transmitted using uplink transmission resources of a previously received uplink transmission resource grant, exceeds a prescribed time, and there is data available for uplink transmission, and no uplink transmission resource grant has been received since transmission of the most recent buffer status report.
 19. The method of claim 18, wherein the uplink transmission resource grant request is a scheduling request (SR).
 20. A secondary station, comprising: a buffer for storing data packets for uplink transmission to a primary station, a transceiver configured to transmit data and control information to a primary station on an uplink channel, the transmission of data requiring a previous grant of an uplink transmission resource from the primary station, the transmission of certain control information not requiring a previous grant of an uplink transmission resource, a processing circuit coupled to the buffer and to the transceiver and configured to: determine if an uplink transmission resource is available; determine if a request condition is satisfied, said request condition being based on (i) at least one previous grant of an uplink transmission resource and (ii) a time elapsed since a previous transmission to the primary station of an indication of the amount of data contained in the buffer when the secondary station has not received a grant of uplink transmission resource since the last transmission of the indication of the amount of data contained in the buffer, cause the transceiver to transmit to the primary station a request to grant an uplink transmission resource when an uplink transmission resource is not available and said request condition is satisfied.
 21. The secondary station of claim 20, wherein the satisfaction of the request condition depends on the time elapsed since the last grant of resource being greater than a threshold.
 22. The secondary station of claim 21, wherein the threshold depends at least on at least one of a set of data characteristics of a data packet in the buffer.
 23. The secondary station of claim 22, wherein the set of data characteristics of a data packet in the buffer comprises at least one of the group of characteristics consisting of: indication of data priority; Quality of Service parameters; identity of a logical channel to which the data packets are assigned; identity of a group of logical channels to which the data packets are assigned; the amount of data in the buffer of the secondary station; the amount of data which arrived at the secondary station; a rate of arrival of data at the secondary station; and the time elapsed since a previous arrival of data.
 24. The secondary station of claim 21, wherein the secondary station operates in a radio cell, and wherein the threshold is based on the time elapsed since the secondary station started to operate in said radio cell.
 25. The secondary station of claim 21, wherein the threshold depends at least on a time elapsed since the secondary station last transmitted a request for an uplink transmission resource.
 26. The secondary station of claim 21, wherein the threshold depends at least on a time elapsed since the secondary station last transmitted a request for an uplink transmission resource corresponding to a specific amount of data and did not receive a corresponding grant of resource.
 27. The secondary station of claim 21, wherein the threshold depends at least on a set of uplink channel characteristics.
 28. The secondary station of claim 27, wherein the set of uplink channel characteristics comprises at least one of the following: an uplink channel quality, a transmission rate corresponding to the uplink channel quality, an uplink transmission power.
 29. The secondary station of claim 27, wherein the set of uplink channel characteristics is estimated based on characteristics related to a downlink channel.
 30. The secondary station of claim 20, wherein the satisfaction of the request condition depends on a quantity of uplink transmission resource allocated in the previous grant of the uplink transmission resource being less than a threshold.
 31. The secondary station of claim 20, wherein the satisfaction of the request condition depends on the average amount of resource allocated in a set of previous grants of uplink transmission resource being less than a threshold.
 32. The secondary station of claim 20, wherein the satisfaction of the request condition depends on the total amount of resource allocated in a set of previous grants of uplink transmission resource being less than a threshold.
 33. A secondary station, comprising: a transceiver configured to transmit data and control information to a primary station on an uplink channel; a buffer configured to buffer data packets to be transmitted to the primary station; and a processing circuit coupled to the buffer and the transceiver, wherein the processing circuit is configured to determine a request condition based on at least one previous grant of uplink transmission resource and a time elapsed since a previous transmission of an indication of an amount of data contained in the buffer without receiving a grant for transmission; the processing circuit being further configured to request, via the transceiver, an uplink grant when the request condition is satisfied.
 34. The secondary station of claim 33, wherein the processing circuit is further configured to determine if the uplink grant is available.
 35. The secondary station of claim 33, wherein the request condition is satisfied when the time elapsed since a previous transmission of an indication of an amount of data contained in the buffer was transmitted using resources of the at least one previous uplink transmission resource grant exceeds a threshold value.
 36. The secondary station of claim 35, wherein the threshold value is determined based on at least one of: at least one characteristic of the data in the buffer, occurrence of a cell change within a defined period preceding the current time, and at least one characteristic of a radio channel employed by the secondary station.
 37. The secondary station of claim 33, wherein the uplink transmission resource grant request is a scheduling request (SR). 